Field of the Invention
The invention relates to a system and a method for providing sound to at least one user, wherein audio signals from an audio signal source, such as a microphone for capturing a speaker's voice, are transmitted via a wireless link to a receiver unit, such as an audio receiver for a hearing aid, from where the audio signals are supplied to means for stimulating the hearing of the user, such as a hearing aid loudspeaker.
Description of Related Art
Typically, wireless microphones are used by teachers teaching hearing impaired persons in a classroom (wherein the audio signals captured by the wireless microphone of the teacher are transmitted to a plurality of receiver units worn by the hearing impaired persons listening to the teacher) or in cases where several persons are speaking to a hearing impaired person (for example, in a professional meeting, wherein each speaker is provided with a wireless microphone and with the receiver units of the hearing impaired person receiving audio signals from all wireless microphones). Another example is audio tour guiding, wherein the guide uses a wireless microphone.
Another application of wireless audio systems is the case in which the transmission unit is designed as an assistive listening device. In this case, the transmission unit may include a wireless microphone for capturing ambient sound, in particular from a speaker close to the user, and/or a gateway to an external audio device, such as a mobile phone; here the transmission unit usually only serves to supply wireless audio signals to the receiver unit(s) worn by the user.
International Patent Application Publication WO 2010/078435 A2 and corresponding U.S. Pat. No. 8,150,057 relate to a communication system comprising a plurality of transmission units having a microphone for capturing the respective speaker's voice and transmitting audio signal data packets to a receiver unit which may be connected to an earphone or to a hearing aid via a plug jack. The transmission units and the receiver unit form a wireless network using a pseudo random sequence frequency hopping scheme and having a master-slave architecture, wherein certain slots in each frame are individually attributed to each of the transmission units, so that each transmission unit is allowed to transmit audio signals in its dedicated slots and receive audio signals transmitted in the remaining slots. Synchronization information data may be transmitted by the master in a certain slot of the frame. Each audio data packet is redundantly transmitted three times in three dedicated slots, with the receiver unit only listening until a correct copy of the audio data packet has been received, so that, when already the first copy is correctly received, the receiver unit would not listen to the redundant copies.
Interference between wireless devices operating the same band, such as the 2.4 GHz ISM band, may be a problem. In general, wireless devices may act as frequency static interferers using always the same frequencies for packet transmission (such WiFi devices) or as frequency hopping interferes using different transmission channels selected randomly from a list of transmission channels (such as Bluetooth devices). In adaptive frequency hopping (AFH), such channel list is regularly updated by removing interfering channels in order to minimize interference and by eventually re-inserting removed channel again once they are no longer interfering.
International Patent Application Publication WO 2012/002978 A1 and corresponding U.S. Pat. No. 8,284,817 relate to a wireless headset for mobile phones using an AFH algorithm, wherein broadband interferers are detected by determining an RSSI (received signal strength indicator) not only on the frequency where a packet is to be received but also on one or more neighboring frequencies/channels.
U.S. Pat. No. 7,995,687 B2 relates to a Bluetooth network using an AFH algorithm, wherein an RSSI is measured, optionally together with a bit error rate of the received packets.
U.S. Pat. No. 7,684,464 B2 likewise relates to a Bluetooth network using an AFH algorithm, wherein the channel metrics, as determined from RSSI and packet error rate measurements, is filtered in order to remove channel metric indicative of frequency hopping interference, so that only channel metrics indicative of frequency static interference remain. The RSSI is compared to threshold values. The filtering includes the formation of channel blocks.
U.S. Pat. No. 8,218,487 B2 relates to Bluetooth network using an AFH algorithm, wherein both an RSSI and a bit error rate are used for channel classification.
U.S. Pat. No. 7,529,288 B2 relates to a Bluetooth network using an AFH algorithm, wherein data packet error rates and/or bit error rates are used for channel classification.
U.S. Patent Application Publication 2012/0076173 A1 corresponds to U.S. Pat. No. 9,136,902 B2 relates to a Bluetooth network using an AFH algorithm, wherein a power spectral density is determined and compared to a fixed threshold for channel classification.